As Ed says, maybe something with more power to asure more shock damage and penetration.
When I was just using my 22 Whisper I had alot of runners, flyoffs, and like you just had, zombie birds. I was begining to think the only sure way to get a kill would be if I saw a mini mushrom cloud hanging over the bird !!
Got the Trail XL and now, almost all are DRT. But even then, there can be the occational runner or flyoff. Had one a few weeks ago. Center breast shot with a Predator. The exit hole in it's lower back was big enough to put a finger in, it still manged to turn 180 degrees and fly off about 30 yards before it dropped.
I have learned that some Starlings can be tough birds ..or they're just too stupid to know when to be dead

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Paul